1. Field of the Invention
The invention relates to a control apparatus and a control method for a vehicular drive apparatus that includes a driving power source, and a power transmission device that transmits power from the driving power source to a drive wheel. More specifically, the invention relates to a technology for determining whether a malfunction occurs in a power transmission device.
2. Description of the Related Art
A control apparatus for a vehicular drive apparatus is available. The control apparatus determines whether a malfunction occurs in a power transmission device provided in the vehicular drive apparatus by making a comparison between the actual rotational speed and the theoretical rotational speed of a predetermined rotational member that constitutes a part of the vehicular drive apparatus. For example, Japanese Patent Application Publication No. 2001-108090 (JP-A-2001-108090) describes a technology in which it is determined whether a malfunction occurs in a shift device by calculating a theoretical value of an output rotational speed of the shift device based on an input rotational speed of the shift device and a speed ratio, and comparing an actual output rotational speed detected by a rotational speed sensor with the calculated theoretical value. Also, Japanese Patent Application Publication No. 2006-220225 (JP-A-2006-220225), Japanese Patent Application Publication No. 10-196779 (JP-A-10-196779), and Japanese Patent Application Publication No. 2002-283880 (JP-A-2002-283880) describe technologies related to the invention.
In the case where it is determined whether a malfunction occurs in the above-described power transmission device, it may be determined that a malfunction occurs in the power transmission device, when it is determined that the power transmission device remains in an abnormal state for a predetermined period. This improves determination accuracy.
However, in the case where the rotational speed sensor detects the actual rotational speed of the rotational member, when the actual rotational speed is in the low rotational speed region, the accuracy of detecting the rotational speed is generally low, and the timing at which the rotational speed is detected is generally delayed, due to the characteristic of the rotational speed sensor, as compared to when the actual rotational speed is in the high rotational speed region. Therefore, for example, if the above-described predetermined period is set to a constant period, it may be erroneously determined that a malfunction occurs although no malfunction occurs when the rotational speed is in the low rotational speed region, or the accuracy of determining that a malfunction occurs may deteriorate when the rotational speed is in the high rotational speed region.
In the case where a predetermined control is started, for example, a fail-safe control that prevents the rotational member from overspeeding is started to improve the endurance of the power transmission device when it is determined that a malfunction occurs in the power transmission device, it is desired to avoid as much as possible the situation where it is erroneously determined that a malfunction occurs and the fail-safe control is executed due to the erroneous determination when the rotational speed is in the low rotational speed region, and it is desired to quickly start the fail-safe control, when the rotational speed is in the high rotational speed region, because a difference between the rotational speed and an overspeed value is small when the rotational speed is in the high rotational speed region.
For example, a power transmission device that includes a differential portion and a shift portion is available. The differential portion includes a first rotational element (first element) connected to an engine, a second rotational element (second element) connected to a first motor, and a third rotational element (third element) connected to a transmitting member and a second motor. The differential portion distributes output from the engine to the first motor and the transmitting member. The shift portion is provided in a power transmission path from the transmitting member to a drive wheel. In the case where the power transmission device with this configuration is used, if there is no load in an area downstream of the transmitting member (i.e., an area which is closer to the drive wheel than the transmitting member is) due to a malfunction relating to the shift portion, the transmitting member and/or the second motor may overspeed. The problem that the transmitting member and/or the second motor may overspeed has not been sufficiently examined. In this regard, when a malfunction relating to the shift portion occurs, the fail-safe control, which prevents the transmitting member and/or the second motor from overspeeding, may be executed. Therefore, it is desired to improve the accuracy of determining that a malfunction occurs when the rotational speed is in the high rotational speed region, and to reduce the possibility that it is erroneously and unnecessarily determined that a malfunction occurs.
The power transmission device that includes the differential portion and the shift portion is an example of the power transmission device. The problem is not limited to a determination as to whether a malfunction occurs in the above-described power transmission device. Another example of the power transmission device may be an engagement device that switches the state of the power transmission path through which power from the driving power source is transmitted to the drive wheel, between a power-transmission permitted state and a power-transmission interrupted state. Naturally, the problem occurs when it is determined whether a malfunction occurs in the above-described engagement device.